linux-kernel - Re: [RFC PATCH v3 26/59] KVM: x86: Introduce vm_teardown() hook in kvm_arch_vm

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Message-ID: <8735nkhre8.ffs@tglx>
Date:   Thu, 25 Nov 2021 22:11:43 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Paolo Bonzini <pbonzini@...hat.com>, isaku.yamahata@...el.com,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     isaku.yamahata@...il.com,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [RFC PATCH v3 26/59] KVM: x86: Introduce vm_teardown() hook in
 kvm_arch_vm_destroy()

On Thu, Nov 25 2021 at 21:54, Paolo Bonzini wrote:
> On 11/25/21 20:46, Thomas Gleixner wrote:
>> On Wed, Nov 24 2021 at 16:20, isaku yamahata wrote:
>>> Add a second kvm_x86_ops hook in kvm_arch_vm_destroy() to support TDX's
>>> destruction path, which needs to first put the VM into a teardown state,
>>> then free per-vCPU resource, and finally free per-VM resources.
>>>
>>> Note, this knowingly creates a discrepancy in nomenclature for SVM as
>>> svm_vm_teardown() invokes avic_vm_destroy() and sev_vm_destroy().
>>> Moving the now-misnamed functions or renaming them is left to a future
>>> patch so as not to introduce a functional change for SVM.
>> That's just the wrong way around. Fixup SVM first and then add the TDX
>> muck on top. Stop this 'left to a future patch' nonsense. I know for
>> sure that those future patches never materialize.
>
> Or just keep vm_destroy for the "early" destruction, and give a new name 
> to the new hook.  It is used to give back the TDCS memory, so perhaps 
> you can call it vm_free?

Up to you, but the current approach is bogus. I rather go for a fully
symmetric interface and let the various incarnations opt in at the right
place. Similar to what cpu hotplug states are implementing.

Thanks,

        tglx